It looks like you might have an automatic discount set up in your admin that's set to give $5 when you purchase 2 of that product (or some similar set up).
Go to your 'Discounts' menu in your admin and see what is listed under the Automatic discounts.
On shopify there are a lot of ways how to get discounts. I tried them on myself and it really works. This is a huge buy/sale platform that always inventing sth new and very profitable. This is really a nice thing because the buyers can save money for the next orders. I found from https://apps.shopify.com/smarty-discounts how to get some extra discounts. Firstly, I thought that it is a spam. I decided to order an Iphone cable adn I paid for it instead of 15 dollars jsut 8. That was really great and I understood that it really works.